The goal of this clinical trial is to learn if ARD-101 works to treat hyperphagia-related behavior in patients with Prader-Willi syndrome (PWS). It will also teach us about the safety of ARD-101. The main questions it aims to answer are: * Does ARD-101 improve the total score of the HQCT-9 (hyperphagia questionnaire for clinical trials, 9 questions)? * What medical problems do participants have when taking ARD-101? Researchers will compare ARD-101 to a placebo (a look-alike substance that contains no drug) to see if ARD-101 works to treat hyperphagia in PWS subjects. Eligible participants will: * Take ARD-101 or a placebo every day for 12 weeks. * Visit the clinic or have a tele-visit once every 2 to 4 weeks during dosing and then have a tele-visit 4 weeks after stopping the ARD-101 or placebo. * Patients/Caregivers will keep a daily diary. Participants who complete the study may be eligible to enter an open-label extension study where everyone will receive ARD-101.